1. Field of the Invention
The present invention relates to a radiography control apparatus and a radiography control method for capturing a radiographic image.
2. Description of the Related Art
Film-screen systems using an intensifying screen and an X-ray film in combination are often used as X-ray machines in hospitals. In this type of system, X-rays pass through an object and are converted into visible light having an intensity proportional to that of the X-rays by the intensifying screen. The X-ray film is exposed to the visible light, and thus an X-ray image can be obtained. The film is observed using an observing apparatus called a viewing box.
Japanese Patent Laid-Open No. 05-064081 discusses an X-ray television apparatus which performs a radioscopic operation in which an X-ray radioscopic image is displayed on a cathode-ray tube (CRT) monitor using an image intensifier. Such an apparatus has come into widespread use in medical applications.
Japanese Patent No. 3066944 discusses a high resolution solid-state X-ray detecting device using a flat panel detector (FPD). In this device, an object is placed between an X-ray source and an X-ray detector. The intensity of X-rays that pass through the object is converted into electrical signals. Thus, digital data representing an X-ray image of the object can be obtained.
Japanese Patent Laid-Open No. 2004-73354 discusses a cassette-type sensor capable of capturing an image using a portable sensor unit has been put to practical use. Japan Industrial Standard (JIS) specifies the degree of coincidence between an X-ray irradiation area and an image-receiving area for X-ray radioscopy using cassette-type sensors (JIS handbook 2005, radiation, T0601-1-3, medical electrical equipment, Japanese Standards Association”.
Japanese Patent No. 3624106 describes a method for easily determining an image-capturing position by emitting electromagnetic waves from an X-ray generating device toward the flat panel detector.
FIG. 24 is a schematic diagram illustrating the relationship between an X-ray flat panel detector and an X-ray irradiation area. In X-ray radioscopy using a cassette-type flat panel detector 1, the flat panel detector 1 is disposed at a predetermined position and an object is placed on the flat panel detector 1 to capture an X-ray image of the object.
The relationship between an irradiation area T of X-rays emitted from an X-ray tube and the flat panel detector 1 is specified as follows. A displacement between the boundaries of the X-ray irradiation area T and the corresponding boundaries of the flat panel detector 1 along two orthogonal main axes of the flat panel detector 1 must be no more than 3% of the distance between the focal point of the X-ray tube and the flat panel detector 1. In addition, the total displacement along the two axes must be no more than 4% of the distance between the focal point of the X-ray tube and an X-ray sensor 13.
The flat panel detector 1 and the X-ray irradiation area T are required to satisfy the following conditions:|x1|+|x2|≦0.03·D |y1|+|y2|≦0.03·D |x1|+|x2|+|y1|+|y2|≦0.04·D where x1 and x2 are displacements between the boundaries of the flat panel detector 1 and the X-ray irradiation area T along the main axis Ax of the flat panel detector 1, y1 and y2 are displacements between the boundaries of the flat panel detector 1 and the X-ray irradiation area T along the main axis Ay of the flat panel detector 1, and D is the distance between the focal point of the X-ray tube and the flat panel detector 1.
According to Japanese Patent No. 3624106, while the position of the flat panel detector 1 can be detected, the X-ray radiographic operation cannot be controlled. This results in an area outside the flat panel detector being irradiated with X-rays.
Also in the invention according to Japanese Patent Laid-Open No. 2004-73354, the X-ray radiographic operation cannot be controlled. In addition, the positional relationship between the X-ray source and the flat panel detector is not taken into account, and X-rays are emitted in the radioscopic operation even when the positional relationship is such that the area outside the flat panel detector can be irradiated with the X-rays.
Even if the positional relationship is such that all of the X-rays are incident on the flat panel detector, there is a risk that the positional relationship will change such that some of the X-rays leak instead of being incident on the flat panel detector for some reason. Also in such a case, the X-rays are continuously emitted in the radioscopic operation.